Some say the movie impulse comes from voyeurism, but I think a case could be made for sado-masochism, especially after watching some of the selections in this year’s Boston Underground Film Festival.

Ann Marie Fleming’s perky and perverse The French Guy (2005; Brattle March 22, 7 pm and March 23, 5 pm, with the director present at the March 22 screening) opens with an extreme close-up of a sutured incision. Elizabeth (Baza Chula) has just had brain surgery. The hospital needs the bed, so she’s handed some pills and a roll of gauze and asked to clear out. She returns to the apartment she shares with Charles, her gay beloved, but since he’s not home, she strolls to the beach and brings home a struggling musician. Maybe it’s just the way Elizabeth tells him that life is beautiful, or maybe it’s the blood-stained bandage on her shaven head that she reveals when she pulls off her wig, but he kisses her. What happens next is horrific and hilarious. And then Charles enters with a string quartet and things get really strange.

This one film justifies the entire festival; even the décor of the apartment, with its large portrait of a plum, marks Fleming as an intense talent. But they all can’t be winners. Bret Wood’s Psychopathia Sexualis (2006; Brattle March 22, 9:45 pm), dramatizes case studies from Kraft-Ebbing’s monumental 19th-century compilation of kinky pastimes. Some of the episodes prove affecting, but the heavy-handed moralizing against Victorian repression and hypocrisy takes the fun out of fetishism, necrophilia, and bondage and discipline.

More to the point is Corey Michael Smithson’s Humoresque (2005; HFA March 26, 7:30 pm). No scientific or moral constraints here, or much in the way of narrative. A 400-year-old Madame, a hobo named Dr. Peacheater, a mysterious gender-non-specific shaman called the Horse Surgeon, and various other characters that look like figures in a Rorschach test get it on in graphic, abstracted debauchery that defies Kraft-Ebbing’s categories. Smithson’s influences range from Guy Maddin to the Keystone Kops, but the poop and the feathers are all his own.

What strikes me most about these films is their innocence and whimsy. The title 6’2” Australian woman of Janet Merewether’s documentary Jabe Babe: A Heightened Life (2005; Brattle March 26, 7:15 pm) suffers from Marfan Syndrome, a life-threatening genetic disorder that causes gigantism. She’s suffered from a lot more as well, including a childhood with a crazy mother and abusive foster homes that rival the made-up stories of “JT LeRoy.” Because she didn’t think she’d live beyond the age of 25 and because she wanted to take control of things, she got into the dominatrix business. All this seems poignant rather than squalid, partly because of Jabe’s personality, partly because of Merewether’s delightful staging, which poses Jabe in tiny model cities like a 50-foot woman, or takes the roofs off toy houses to reveal tiny TVs on which she relates the story of one foster home or the other. Medical advances have now made it likely that Jabe will enjoy a normal life expectancy. So she’s pursuing a normal occupation — in the funeral industry.